Asthma may be considered one of the most preventable conditions necessitating frequent use of acute care services. To prevent hospitalizations and emergency department visits, it may be important for physicians to obtain an accurate assessment of a subject's asthma symptom control. A subject's perception and caretaker's (e.g., a parent or guardian) perception of asthma control of the subject may vary tremendously and frequently may not correlate with objective measures. In one study, 21% of parents described their children's asthma as very well controlled, and yet the child had visited the emergency room or required an acute outpatient visit for asthma in the last three months. With varying asthma phenotypes, poor asthma-control perception, and growing costs of asthma, adequate asthma-control measures are important.